The invention relates to a method for testing tires and to an apparatus for implementation thereof, intended in particular but not exclusively for tires of heavy road haulage vehicles (lorries and the like).
A phenomenon typically affecting these kinds of tires (alternatively spelled xe2x80x9ctiresxe2x80x9d) consists of the breaks which reveals itself as a clean cut on the side of the tire (alternatively spelled xe2x80x9ctirexe2x80x9d), extending circumferentially thereto and along which a cutting-off of the radial cords forming the carcass of the tire occurs. This phenomenon is known to persons skilled in the art by the name of xe2x80x9czipper break.xe2x80x9d
The reinforcing cords of tire carcasses for heavy road haulage generally consist of metallic wires and are much stronger than textile cords commonly used in the carcasses of car tire. As a results it is difficult to understand how this type of break occurs, especially when taking into account that failure may occur after only a short distance traveled by the tire.
In other words, said xe2x80x9czipper breakxe2x80x9d cannot be attributed to the normal wear to which a tire is subject following prolonged use over time or in particularly severe conditions (heavy load, rough road surface, etc.), and does not fall within the other known forms of tire breaks.
Consequently, it is difficult, if not impossible, to understand and reproduce with the usual methods (computer analysis, experiments, etc.) the conditions thatxe2x80x94in real driving conditionsxe2x80x94lead to the xe2x80x9czipper breakxe2x80x9d of tires. Additionally, this problem renders it difficult, if not impossible, to provide tire structures for lorries and the like specifically designed to prevent this particular type of break.
The present invention aims at remedying this situation.
The invention arises from Applicant""s perception that the xe2x80x9czipper breakxe2x80x9d is caused by abnormal and occasional working conditions of the sidewall of the tire, capable of causing a particular fatigue stress in the carcass structure.
An example of these stresses is the so-called xe2x80x9ckissingxe2x80x9d, i.e. the interference which occurs between two tires mounted side by side on the same axle (such as the twinned tires in the lorries) in the event of an excessive load acting on them, or when one of the tires is operating with an inflation pressure lower than that of the other tire or both the tires have a pressure which is lower than the nominal operating pressure.
Therefore, on the basis of said perception, the present invention provides a method for testing tires and an apparatus for carrying out said method, suitable for reproducing the conditions which, during use, give rise to the phenomenon of xe2x80x9czipper breakxe2x80x9d.
The characterising features of said method and of the abovementioned apparatus are set out in the following claims.